1. Field of the Invention
The invention relates to a urological implant, in particular a vascular wall support for the urinary tract, such as a urethral, prostate or ureter stent, comprising a substantially tubular, inherently stable carrier. Vascular wall supports of the generic type, which are usually designated as "stents" in technical terminology, are as a rule used for dilating and keeping open pathologically closed or stenotic body vessels. Further examples of application for the urological implants specified are urinary catheters, artificial ureters, artificial urinary diversion systems correspondingly completed by a bladder and so forth.
2. Background Art
To simplify matters, the stents mentioned above will be dealt with below by way of example in the discussion of the prior art and the invention:
Urethral, prostate and ureter stents are indispensable implants for patients with disorders of the urinary tract, if these patients are not in the shape and condition for corresponding surgery. A great variety of stent designs and materials are available today. As a rule, design and material depend on the place where the stent is used and on the implantation technique used. For instance, tubular carriers made from an expansible lattice material are customary. The stent is inserted in its contracted condition via a catheter into the corresponding vessel, where it is expanded for instance by the action of a bubble, its lattice structure extending and the vessel thus being dilated. The stent remains at the place of implantation, serving to support the vascular wall against renewed stenosis.
A serious problem resides in that with all the materials used and tested so far for urinary tract stents, crystallization processes and bacterial colonization will occur on the surface of the stent after several weeks of contact with urine. This leads to serious malfunction of the implants, which strongly jeopardizes the medical success of stent implantation. Numerous studies have dealt with various materials of medicinal technology such as titanium, stainless steel and polymers. However, really durable resistance to crystallize has not been found in any material.
An example of corresponding prior art measures can be seen from U.S. Pat. No. 5 328 954. This document discloses an encrustation and bacterial resistant coating for use on medical devices. The coating includes a reaction product formed by covalent linkage of a hydrophilic polyurethane pre-polymer and aminopolycarboxylic acid. A urease inhibitor and/or antibacterial agent may also be added to the coating.
The aim of this coating--namely to render surfaces resistant to encrustations--is pursued, using antibacterial substances which are bonded on the surface, there preventing a pH increase as produced by bacterial colonization. In this case, encrustations are to be blocked by precipitation of the urine components no longer taking place due to an increased pH.
The substances specified for immobilization are among others ethylene-diamine-tetra-acetate complexes, antibiotics and silver ions, which are ionically or covalently bonded to polyurethanes. As has however been found, the blocking of encrustations achievable by this prior art is still in need of improvement. It is an object of the invention to solve these problems.